Compressor and vacuum pump



Dec. 23, 1941. F. BAsr l COMPRESSOR AND VACUUM PUMP Filed May 1 1940 2sheets-sheet 1 Patented Dec. 23, 1941 COMPRESSOR AND VACUUM PUMP Leon F.Bast, Allentown, Pa., assignor to Fuller A Company, Catasauqua, Pa., acorporation of Delaware Application May 1, 1940, sel-iam. 332,627 aclaims. (CL 23o-151) This invention relates to rotary air compressorsand vacuum pumps which include a stator casing having a cylindrical boreclosed by heads and a rotor carrying radially sliding vanes and mountedeccentrically within the bore on a shaft extending into openings intheheads. More particularly, vthe invention is concerned with a novel meansfor sealing the shaft of such a machine in order to prevent flow` offluid along the shaft to or from that part of the space within the borenot occupied by the rotor. As will be readily apparent, the new sealingmeans is applicable to both compressors and pumps, but in order tosimplify the disclosure, its use in connection with an air compressoronly will be described in detail.

Air leakage through the clearance spaces between the rotor shaft and thewalls of the openings in the cylinder'heads of a rotary air compressorresults in a substantial loss in etliciency and although various meanshave been employed heretofore for reducing that leakage, thoseexpedients have not been wholly satisfactory. The

and there will be no blnding'of the ring as a result of expansionproduced by heat generated during operation.- The mounting vfor the ringmakes only lateral contact therewith under normal conditions and thepreferred mounting takes the form of a retainer fast on the shaft andhaving a circumferential groove or channel in which the ring lies, theinner surface of the ring being spaced substantially from the bottom ofthe groove. The ring bears laterally against one or both side walls ofthe groove and is held in contact therewith eitherwholiy by the pressuredif` problem presented is that of obtaining substantially completesealing of the shaft in its openings by means Which will not besubjected to considerable wear and will, at the same time, permit alimited radial movement of the shaft within the openings and beunaffected by expansion of the parts as they become heated duringoperation.

In one prior construction, hub collars mounted on the shaft within theopenings are employed to reduce the leakage, but when such collars areused, there must be clearances between them and the walls of theopenings'to allow for the radial movement of the shaft resulting fromwear and the expansion of the parts when heated. This clearance isnecessarily of such s ize that the collars fall far short of sealingtheshaft and the eiciency of a compressor equipped with collars issubstantially reduced by the leakage past them.

The present invention is, accordingly, directed to the provision of aseal for the shaft of a. rotary air compressor or vacuum pump of thesliding vane type which not only effectively prevents leakage alongtheshaft but is also so constructed as to have a long life and becapable of Vuse for indefinite periods without' attention orreplacement.

The seal of the invention comprises a. split sealing ring which ismounted on the shaft to rotate therewith vand has an outer -peripheralsurface making a sliding contact with the wall ofv the opening. Theinner diameter of the ring is greater than that of the parts lyingwithin-it, so that radial movement of the shaft may take place ferentialon opposite faces of the ring during operaon or partly by' thatdifferential and partly by the inherent springiness of the metal ofwhich the ring is made. Inone form, the pressure with which the ringbears laterally against one or both faces of the groove is sumcient toovercome the friction between the peripheral surface4 of the ring andthe Wall of the opening, so that the ring'v Ina diiferent form, Y

rotates -with the retainer. rotation of the ring with the retainer isinsured by the provision of a positive connection between these parts.

For some purposes, a single ring in each opening may be suicient toprovide a seal, but, if desired, each sealmay comprise a pair of ringsmounted in separategrooves in the retainer..

When the doublevring construction is employed, means are provided forpermitting the escape vfrom the space between the rings of fluid orother material which passes through the opening in the inner ring andenters that space.

For a better understanding of the invention, reference may be made tothe accompanying drawings, in which:

Fig. l is a vertical section through one form of air compressor equippedwith the seal of the, in-

vention;

Fig. 2 is a fragmentary verticaly sectional view illustrating a seal ofmodified construction;

Fig. 3 is a. vertical sectional ViewV through a portion of thecompressor equipped with the new seal and provided with a bearingdifferent from lthat shown in Fig. l;

Fig. 4 is a view in perspective of one end of 'a compressor equippedwith the seal of the invention and having its adjacent head removed;

Figs. 5 and 6 are front and rear elevational,

views of one type'of ring employed in the new seal;

Figs. 8 and 9 are side and edge views, respectively, of another type ofring which may be employed in the new seal; and

Fig. 10 is a fragmentary sectional view showing a modified sealconstruction.

Referring to the drawings, the compressor illustrated includes a statorcasing I having an air inlet 2 at one side, an air outlet 3 at theopposite side, and a cylindrical bore 4 to and from which the inlet andoutlet, respectively, lead. Within the bore is a cylindrical rotor 5provided with radial slots 6 in which are slidably mounted vanes orblades l.. lies eccentrically within the bore so that the surface of`the rotor is suflic'ziently close to the inner surface of the bore atone point between the inlet and outlet to form a seal opposite which isa crescent-shaped space. This space is subdivided into compartments bythe vanes which are moved out of their slots centrifugally as the rotorturns and slide along the inner surface of the bore, and air enteringthrough the inlet enters the compartments and is compressed as thecompartments decrease in size as they approach the outlet. i

The rotor shaft is provided with trunnions 8 and 9 which rotate inbearing assemblies I0 and I I mounted in heads I2 and I3 which aresecured to the ends of the casing and have inner faces I 4, I5 closingthe ends of the bore. The heads are formed with openings I6, II throughwhich the shaft extends from the end of the rotor to the trunnions andthe openings have enlargements with inner circumferential faces I8, I9.The outer surfaces of the bearing assemblies contact with faces I8, I9,and the bearings are axially adjustable by means of shms 20 and 2Iinterposed between the bearing assemblies and portions of the heads I2,I3. The bearing structure illustrated is that disclosed in RedfieldPatent No. 1,994,786, issued March 19, 1935, but other types of mountingfor the rotor shaft may be employed, if desired.

The diameter of the openings I6, II through The rotor is mounted on ashaft and used, if desired. The ring has an outside diameter notsubstantially less than the diameter of the opening in the casing headso that when mounted in place in its retainer, it makes a close slidingcontact with the wall of the opening. The ring has no tendency to expandor contract radially and it is peened, as indicated at 26, ap-

proXimately half Way around on one side and similarly treated, asindicated at 21, on the other which the rotor shaft extends issubstantially greater than that of the shaft and leakage through thespace around the shaft in each opening is prevented by a seal. Each ofthe seals illustrated comprises a retainer 22, 23 which is ofcylindrical form and is mounted fast on the shaft in any suitablemanner, as by being shrunk on. Each retainer has an outer diametersufficiently less than the diameter of the opening in which 4it lies topermit such radial movement of the shaft in the bearings as results fromwear plus expansion of the parts resulting from heat developed whenrunning. Each retainer is formed with a circumferential groove or slot24 which is of substantial depth and mounted within the slot is a splitsealing ring 25 which has an inner diameter substantially greater thanthe diameter of the bottom of the groove and makes contact on its outerperipheral surface with the wall of the opening. The provision of thespace between the inner surface of each ring and the bottom of thegroove in which it is mounted permits the ring to move radially withrespect to the retainer as radial movement of the shaft occurs and alsoprevents expansion of the shaft and retainer from interfering with theaction of the ring.

-Two general types of ring may be employed for the purpose and theseringsmay, for convenience. be referred to as live or dead rings.

'I'he ring shown in Figs. 5, 6, and? is of the dead type and it mayconveniently be made of cast iron, although other lkinds of metal may being to force it against the outer lateral face of Y side, the peening onopposite sides of the ring being on opposite sections thereof. The ringis cut at an angle, as indicated at 28, and the peening causes it toassume a slightly helical form so that its overlapping ends are normallyspaced, as indicated at 29. In the construction described, the ring hasbeen caused to assume a helical form, when relaxed, by peening, but itmay be given the desired shape in any other way, if desired.

When this ring is mounted in the groove in the retainer, the tendency ofits ends to separate causes the lateral surfaces of the ring to bearagainst the side walls of the groove. This pressure is supplemented bythe differential pressure developed on opposite lateral surfaces of thering during operation, and the forces thus active in holding the ringagainst the side Walls of the groove are suicient to overcome thefriction between the 'outer peripheral surface of the ring and the wallof the opening. The ring, accordingly, rotates with the retainer andshaft and little or no Wear occurs on the lateral surfaces of the ring.Similarly, little wear occurs on the the rear lateral surface of thering and tends to force the ring against the lateral surface of thegroove near the compressor chamber. If the bearing chamber is vented tothe atmosphere, the pressure within the compressor chamber forces thering against the outer surface of the groove.

As an example of the conditions of operation, the following may begiven. In a single V stage compr ssor with a closed bearing chamber andoperating to develop 50# line pressure per sq. in.,

the air at the compressor inlet is at atmospheric` pressure and at theoutlet, its pressure is 50#,

so that on the side of the ring facing the compressor, the pressurevaries from zero to 50#. Because of the leakage between the ends of theseal, a pressure of approximately 45# is built up in the bearing chamberand this pressure acts uniformly over the entire outer surface of thering exposed beyond the groove.

The back pressure is opposed by that within the compressor chamber, butis exceeded thereby only in a region near the outlet. The result is thatthroughout the greater portion of its circumference, the inner lateralface of the ring is held against the inner face of the groove andthrough a minor portion of its circumference near the outlet, the ringis exposed to a pressure tendthe groove. Accordingly, the differentialpressure plus that produced by the ends of the ring being forced intocontact with the walls of the groove bythe inherent springiness of themetal causes the ring to rotate with the shaft. As there is nosubstantial relative movement between the lateral surfaces of the ringand the walls of the groove, there is no lateral wear on the ring. Also,since the ring is dead and its initial outside diameter issubstantially'that of the diameter of the opening, only a slight amountof wear takes place on. the peripheral surface Y of the ring before thering reaches a condition in which it makes a smooth running vfit withthe wall of the opening and thereafter, the ring continues to rotatewith the retainer with practically no wear.

Instead of using the ring of helical form illustrated in Figs. 5, 6, and7, a dead ring. of the plane type shown in Figs. 8 and 9`and having aradial cut 30 may be employed for low pressure operaplane type of deadring is useful in low pressure devices only.

'I'he seal of the invention has proven highly satisfactory in practiceand tests have demon'- strated its marked superiority over close fittinghub collars on the shaft as a means for reducing leakage. In those testsinvolving the use of a two-stage compressor, it was found that themachine, when provided with hub collars, operated with a volumetricefficiency around 85% and that its efficiency increased to overk 90%when the new seals were installed, the efficiency reaching 94% in one ofthe tests. During those tests, the seal rings showed no appreciable wearand had an indicated life of indefinite duration.

I claim:

l. In a'rotary compressor or vacuum pump l which includes a casinghaving a cylindrical bore closed at its ends by heads having alignedopenings, and a rotor provided with sliding vanes and mountedeccentrically within the bore on a shaft extending into the openings,the improvement in sealing means for the shaft in'one opening However,when such a ring is used l inner surface of the ring and the bottom ofthe groove suicient to expand the ring and cause it to be held in suchrm contact with the wall of the opening that the ring remainsstationary. In that case, the ring is worn on its lateral surfaces andfor that reason, the plane type of ring is not desirable for highpressure operation. The expansion referred to also takes place with ahelical ring,v but the differential'pressure plus that resulting fromthe springiness of the metal is sumcient to overcome the peripheralfriction and the ring, accordingly, continues to rotate.

When it is desired to use a pair of rings in the seal, a retainer 3l maybe employed having a pair of grooves 32, 33, the surface of the retainerbetween the grooves being channeled to provide a discharge groove 34, Inthe main grooves are mounted seal rings 35, 36 which contactperipherally with the wall of the opening in the head 31. The head` isthen provided with a bore 38 leading from groove 34 to an opening 39 sothat any material which is entrained with the air and passes through theopening in ring 36 enters the dischargegroove and escapes through thebore.

The live type of ring, which may be used in the new seal, is similar tothat shown in Figs. 8 and 9 and has a radial opening 30. This ring has atendency to expand radially and may be .givenl that characteristic bypeening the ring on its inner face. When such a ring is employed, asindicated at 40 in Fig. 10, provision is made for positively connectingthe ring to Athe retainer. For this purpose, the retainer 4i may bebored so that a pin 42 may be driven through an opening in the ring orbetween the ends thereof and into a recess 43 inthe wall of the groove.The forced rotation of such a ring causes its peripheral face 44 to wearaway until the inherent radial expansion. of the ring is so slight thatthe friction between the peripheral surface -and the wallof the openingis insufficient to cause additional wear. `A live ring may be employedin either high or low pressure machines and the positive connectionbetween the ring and retainer may `be used both with a live ring andAalso with the-dead rings described. .The helical dead ring whichcomprises a ring retainer fiXedly secured -on the shaft within theopening and spaced therefrom, the retainer having a groove in its outerperiphery, and a seal ring in the groove,

A said ring being in its relaxed condition and making a close slidingcontact with the wall of the opening and having no tendency to expandradially outwardly or to contractradially inwardly, the ring having aradial thickness less than the radial distance between the base of thegroove and the wall of the opening, whereby thek ring is fioatinglycarried in said groove and has a limited freedom of movement radially inthe retainer and is free to travel with the retainer when the pressuresupon the opposite sides thereof are suiiiciently unbalanced to cause thefrictional contact between atleast one side ofthe ring and at least oneside of the groove to be greater than the frictional contact between'the periphery of the ring and the wall of the opening.

2. In a rotary compressor or vacuum pump ings, and a rotor provided withsliding vanes and mounted eccentrically within the bore on a shaftextending into the openings, the improvement in and the live ringpositlvelyconnecte'd to ythe retainer may, accordinglybe usedinterchangeably in machines operating at al1 pressures while the sealingmeans for the shaft in one opening which comprises a ring retainer xedlysecured on the shaft within the opening and spaced therefrom, theretainer having a groove in its oter periphery, a-seal ring in thegroove, said ring being in its relaxed condition and making a closesliding Acontact with the wall of the opening and having no tendency toexpand radially outwardly or to contract radially inwardly, the ringhaving a radial thickness less than the radial distance between the baseof the groove and the wall of the opening, whereby the ring is oatinglycarried in said groove and has a limited freedom of movement radially inthe retainer and ls free to travel `with the retainer when the pressuresupon the opposite sides thereof are sufficiently unbalanced to cause thefrictional contact between at least one' side of the ring and at leastone side of the groove to be greater than the frictional contact betweenthe periphery of the ring and-the wall of the opening, and a pin havinga portion extending into the groove to prevent relative rota- .tion ofthe ring and shaft while permitting said limited radial .-movement;

3. In a rotary compressor or vacuum pump which includes a casing havinga cylindrical bore closed at its ends by heads having aligned openings,and a rotor provided with sliding vanes and mounted eccentrically withinthe bore on a shaft extending into the openings, the improvement insealing means for the shaft in one opening which comprises a ringretainer fixedly secured on the shaft within the opening and spacedtherefrom, the retainer having a groove in its outer periphery, and aseal ring in the groove, said ring being peened on at least one of itslateral sides to give it a helical form and having an'outside relaxeddiameter such that it is maintained in close sliding contact with thewall of the opening and has no tendency to expand radially outwardly orto contract yradially inwardly, the ring having a radial thickness lessthan the radial distance between the base of the groove and the Wall ofthe opening, whereby the ring is oatingly carried in -said groove andhas a limited freedom of movement radially in the retainer and is freeto travel with the retainer when the pressures upon the opposite sidesthereof are suiciently unbalanced to cause the frictional contactbetween' at least one side of the ring and at least one side of thegroove to be greater than the frictional contact between the peripheryof the ring and the wall of the opening.

LEON F. BAST.

